Pouches or bags made from polymeric films have found widespread use in a variety of applications. The film is formed by hot extrusion of resin, such as blow-extrusion of a tube, and the tube is slit longitudinally along one side, cut into sections and folded into the desired shape. The unattached free edges are then bonded together, usually by heat sealing, wherein contiguous surfaces of the material are bonded together with the application of heat and pressure.
In a typical heat sealing process, facing surfaces of the film material are pressed together and heated, which causes the material to fuse together and form an autoadhesive bond. The strength of the seal obtained is a function of several factors, including the nature of the materials employed, the temperature and pressure at the material interface, the thickness of the material, and the dwell time, or the period of time during which the assembled materials are exposed to the elevated temperatures and pressures. It is known that films of low density homoand copolymers of ethylene are easily handled, and form reliable high strength welds at relatively low temperatures in excess of 250.degree. F and at very short dwell times, usually in a fraction of a second. The ability to obtain a reliable high strength seal is extremely important to assure maximum utilization of high speed, automated processing equipment that is currently available.
Other materials, while having highly desirable characteristics, are not sufficiently autoadhesive to form reliable heat seals within a reasonable time or otherwise have undesirable surface properties for a particular application. For example, ionomer films provide excellent puncture resistance but are not easily heat sealed with conventional equipment and do not provide a surface which is receptive to printing. Pigmented polyethylene films provide opacity and desirable coloration, but the pigments therein interfere with the formation of a reliable heat seal. Polyamide films and high density polyethylene are also difficult to heat seal under normal conditions but have excellent strength properties.